Eldonia is a soft-bodied animal of unknown affinity,[3] best known from the Fossil Ridge outcrops of the Burgess Shale, particularly in the 'Great Eldonia layer' in the Walcott Quarry.[4] In addition to the 550 collected by Walcott,[5] 224 specimens of Eldonia are known from the Greater Phyllopod bed, where they comprise 0.43% of the community.[6] Species also occur in the Chengjiang biota,[2] and in Upper Ordovician strata of Morocco. Walcott's original interpretation as a holothurian was rapidly disputed.[7] Alternative affinities to be suggested, which did not stand the test of time, included the siphonophores[8][9][10] and a coelentrate medusa.[11] It takes the form of a round, medusoid disk (which originally led to suggestions of a jellyfish affinity)[12] with a C-shaped gut trace. The gut is recalcitrant and can be extracted using HF acid.[13] The organism is frequently found in association with the lobopod Microdictyon, which is presumed to have fed on Eldonia.[14]

The eldoniids form a clade that also includes Paropsonema, Rotadiscus, and Stellostomites.[15]

In Popular Culture

Two Eldonias appeared in the end of the Scavengers when there was a dead Sidneyia and the giant trilobite and a Opabinia eat the dead Sidneyia from the Website The Burgess Shale in the Virtual Sea Odyssey.